1. Field of the Invention
The present invention relates to cyanoadamantyl compounds, polymers that comprise polymerized units of such compounds, and photoresist compositions that comprise such polymers. Preferred polymers of the invention have at least one or two distinct repeat units in addition to cyanoadamantyl units and are employed in photoresists imaged at wavelengths less than 250 nm such as 248 nm and 193 nm.
2. Background
Photoresists are photosensitive films used for transfer of images to a substrate. A coating layer of a photoresist is formed on a substrate and the photoresist layer is then exposed through a photomask to a source of activating radiation. The photomask has areas that are opaque to activating radiation and other areas that are transparent to activating radiation. Exposure to activating radiation provides a photoinduced chemical transformation of the photoresist coating to thereby transfer the pattern of the photomask to the photoresist-coated substrate. Following exposure, the photoresist is developed to provide a relief image that permits selective processing of a substrate.
While currently available photoresists are suitable for many applications, current resists also can exhibit significant shortcomings, particularly in high performance applications such as formation of highly resolved sub-quarter micron and even sub-tenth micron features.
Consequently, interest has increased in photoresists that can be photoimaged with short wavelength radiation, including exposure radiation of below 200 nm such as 193 nm.
Polymers that contain alicyclic groups such as norbornyl are of interest as resin components for photoresists imaged at sub-200 nm wavelengths due to the relatively low absorption of such resins to exposure radiation. See U.S. Pat. No. 6,509,134; T. Wallow et al., Proc. SPIE 2724 (1996) 334; S. J. Choi, et al., J. Photopolymer Sci. Technology, 10 (1997) 521; S. J. Choi et al., Proc. SPIE 3999 (2000) 54; U.S. Pat. Nos. 5,843,624; 6,306,554; and 6,517,990; and Japanese Published Application 2003-12207.
Efforts to enhance transparency for short wavelength exposure can negatively impact other important performance properties such as substrate adhesion and resistance to etchants employed after development, which in turn can dramatically compromise image resolution. In particular, reducing aromatic (e.g. phenyl or substituted phenyl such as phenol) content of a resist to thereby increase transparency at sub-200 nm exposures can provide a resist that exhibits any of poor resistance to plasma etchants used to process substrate surfaces bared upon development, poor adhesion to an underlying substrate, and poor (narrow) lithographic processing windows. See, for instance, U.S. Pat. No. 6,479,211.
Various efforts have been made to improve performance of such short-wavelength photoresists. Certain use of photoresist resins that have certain cyano substitution has been reported. See U.S. Published Applications 2003/0186160 and 2003/0008502; and Japanese Published Applications 2003-122007 and 2004-29542. Highly useful photoresists that comprise a resin with cyano groups are disclosed in U.S. Pat. No. 6,692,888 assigned to the Shipley Company.
It thus would be desirable to have new photoresist compositions, particularly resist compositions that can be effectively imaged at short wavelengths such as sub-250 nm exposure wavelengths.